A conventional field effect transistor has a two-dimensional shape in which a channel is formed on top of a flat surface of a semiconductor. However, recently, in order to improve features of a high speed operation and a low power consumption, a three-dimensional transistor in which a gate insulating film is provided so as to surround a fin-shaped semiconductor portion and a gate electrode is provided so as to surround the gate insulating film (see, e.g., Patent Document 1) starts to be practically used. The gate insulating film is made of, e.g., a high dielectric constant material (high-k material). As for the high dielectric constant material, there is known TiO2, ZrO2, HfO2 or the like (see, e.g., Patent Document 2).
In the fin-shaped semiconductor portion, a transistor of a type in which two opposite side surfaces serve as carrier transfer channels is referred to as a double-gate transistor, and a transistor of a type in which a top surface as well as the two side surfaces serve as carrier transfer channels is referred to as a tri-gate transistor. There is suggested a semiconductor device having the double-gate transistor and the tri-gate transistor on a common substrate while utilizing advantages of the double-gate transistor and the tri-gate transistor (see, e.g., Patent Document 3).
The fin-shaped semiconductor portion protrudes from the substrate. Therefore, if the fin-shaped semiconductor portion is coated by the gate electrode, the corresponding semiconductor portion and the gate electrode have a part having a convex cross-sectional shape which is vertically formed on the substrate. In order to achieve insulation or protection, side surfaces of the part having a convex cross-sectional shape need to be coated by the insulating film.    Patent Document 1: U.S. Pat. No. 7,560,756    Patent Document 2: U.S. Pat. No. 7,714,397    Patent Document 3: U.S. Patent Application Publication No. 2010/0297838
In the case of forming the insulating film on the substrate including the part having a convex cross-sectional shape, the side surfaces of the part having the convex cross-sectional shape needs to be coated by the insulating film. However, a peripheral flat surface or a top surface of the part having a convex cross-sectional shape may not need to be coated by the insulating film because it decreases the flatness of the entire device and increases the thickness of the device. The present inventors have found that it is difficult to selectively coat the part having a convex cross-sectional shape because portions on the side surfaces are removed when portions on the flat surface of the insulating film are removed by plasma etching.